Chemicals for the Removal of Lake Weeds

Chemical Types

• There are a number of herbicides that are specified for use in water. These chemicals include chelated copper compounds, glyphosate, diquat, 2,4-D, copper sulfate, fluridone or endothall. All chemicals are sold under different trade names. Avoid using copper-based herbicides excessively as they may be toxic to fish.

Timing

• The best time to apply herbicides is during late spring during the rapid growth period of the plants. Improperly timed application of even the most effective chemical often reduces its efficacy. Actively growing plants absorb and translocate the chemicals more rapidly through the plant tissues. This process tends to slow down once a plant has reached maturity and during the slower growth periods, such as end of summer or fall.

Water Temperature

• The temperature of the water also affects the efficacy of the chemical. Weeds in a water body are least affected in cold water. Ideal water temperature is 60 degrees Fahrenheit and preferably higher. This is usually between late April and early June. Avoid using herbicides in a lake or pond in later summer as this poses a serious threat to the fish in the water, warns the University of Kentucky Extension.

Amount

• Using the right amount of chemical will help to reduce damage to fish, reduce waste of herbicide and provide greater level of weed control. The herbicide labels generally indicate dosage per acre-feet of the lake or pond. This acreage is calculated by multiplying surface area by the depth of water. A 4-foot-deep water body with a surface area of ½ acre is 2 acre-feet.